Human Renal Cortical Epithelial Cells Research Articles

Modified Zhenwu Tang delays chronic renal failure progression by modulating oxidative stress and hypoxic responses in renal proximal tubular epithelial cells

BackgroundTubulointerstitial fibrosis (TIF) is a critical pathological feature of chronic renal failure (CRF), with oxidative stress (OS) and hypoxic responses in renal proximal tubular epithelial cells playing pivotal roles in disease progression. This study explores the effects of Modified Zhenwu Tang (MZWT) on these processes, aiming to uncover its potential mechanisms in slowing CRF progression. MethodsWe used adenine (Ade) to induce CRF in rats, which were then treated with benazepril hydrochloride (Lotensin) and MZWT for 8 weeks. Assessments included liver and renal function, electrolytes, blood lipids, renal tissue pathology, OS levels, the hypoxia-inducible factor (HIF) pathway, inflammatory markers, and other relevant indicators. In vitro, human renal cortical proximal tubular epithelial cells were subjected to hypoxia and lipopolysaccharide for 72 h, with concurrent treatment using MZWT, FM19G11, and N-acetyl-l-cysteine. Measurements taken included reactive oxygen species (ROS), HIF pathway activity, inflammatory markers, and other relevant indicators. ResultsAde treatment induced significant disruptions in renal function, blood lipids, electrolytes, and tubulointerstitial architecture, alongside heightened OS, HIF pathway activation, and inflammatory responses in rats. In vivo, MZWT effectively ameliorated proteinuria, renal dysfunction, lipid and electrolyte imbalances, and renal tissue damage; it also suppressed OS, HIF pathway activation, epithelial-mesenchymal transition (EMT) in proximal tubular epithelial cells, and reduced the production of inflammatory cytokines and collagen fibers. In vitro findings demonstrated that MZWT decreased apoptosis, reduced ROS production, curbed OS, HIF pathway activation, and EMT in proximal tubular epithelial cells, and diminished the output of inflammatory cytokines and collagen. ConclusionOS and hypoxic responses significantly contribute to TIF development. MZWT mitigates these responses in renal proximal tubular epithelial cells, thereby delaying the progression of CRF.

IDENTIFYING SENOLYTIC TARGETS OF DIETARY FLAVONOIDS IN RENAL CELLS BY THERMAL PROTEOME PROFILING

Abstract Senescent cell accumulation is a known driver of aging and age-related pathologies. Clearance of senescent cells is a promising approach to increase longevity and reduce multiple age-related diseases in humans. Flavonoid compounds are present in fruits and vegetables, of which certain flavonoids (e.g., quercetin and fisetin) have demonstrated senolytic, or ‘senescent-cell-killing’, activity in culture and in mice. However, the cellular mechanism of senolysis and the efficacy of these compounds are not known in renal epithelial cells. Here, we combine flavonoid drug screening, targeted metabolomics, and thermal proteome profiling (TPP) with analysis by mass spectrometry (MS) to explore protein targets of senolytic drugs in senescent human renal cortical epithelial cells and human renal proximal tubular epithelial cells. Senescence was induced by exposure to ionizing radiation and the senescence phenotype was validated through a rigorous panel of senescence and viability markers. Proliferating and senescent renal epithelial cells were screened with a panel of 8 flavonoids to identify senolytic drugs and their concentrations for selectively killing senescent cells. Targeted MS assays were developed to assess intracellular drug uptake, a potential mechanism of senescent-specific killing. To identify protein targets of the senolytic flavonoids in senescent cells, we performed a variation of TPP in combination with liquid chromatography (LC)-MS/MS proteomics analysis, carefully controlling for non-senolytic interactions by excluding proteins bound by a non-senolytic flavonoid. The results of this study pave the way for the development of a more specific generation of senolytic compounds and identify novel candidate senolytic pathways engaged by dietary flavonoids.

Exploiting generative self-supervised learning for the assessment of biological images with lack of annotations

MotivationComputer-aided analysis of biological images typically requires extensive training on large-scale annotated datasets, which is not viable in many situations. In this paper, we present Generative Adversarial Network Discriminator Learner (GAN-DL), a novel self-supervised learning paradigm based on the StyleGAN2 architecture, which we employ for self-supervised image representation learning in the case of fluorescent biological images.ResultsWe show that Wasserstein Generative Adversarial Networks enable high-throughput compound screening based on raw images. We demonstrate this by classifying active and inactive compounds tested for the inhibition of SARS-CoV-2 infection in two different cell models: the primary human renal cortical epithelial cells (HRCE) and the African green monkey kidney epithelial cells (VERO). In contrast to previous methods, our deep learning-based approach does not require any annotation, and can also be used to solve subtle tasks it was not specifically trained on, in a self-supervised manner. For example, it can effectively derive a dose-response curve for the tested treatments.Availability and implementationOur code and embeddings are available at https://gitlab.com/AlesioRFM/gan-dl StyleGAN2 is available at https://github.com/NVlabs/stylegan2.

Exosomes released from Shiga toxin 2a-treated human macrophages modulate inflammatory responses and induce cell death in toxin receptor expressing human cells.

Shiga toxins (Stxs) produced by Stx-producing Escherichia coli are the primarily virulence factors of hemolytic uremic syndrome and central nervous system (CNS) impairment. Although the precise mechanisms of toxin dissemination remain unclear, Stxs bind to extracellular vesicles (EVs). Exosomes, a subset of EVs, may play a key role in Stx-mediated renal injury. To test this hypothesis, we isolated exosomes from monocyte-derived macrophages in the presence of Stx2a or Stx2 toxoids. Macrophage-like differentiated THP-1 cells treated with Stxs secreted Stx-associated exosomes (Stx-Exo) of 90-130 nm in diameter, which induced cytotoxicity in recipient cells in a toxin receptor globotriaosylceramide (Gb3 )-dependent manner. Stx2-Exo engulfed by Gb3 -positive cells were translocated to the endoplasmic reticulum in the human proximal tubule epithelial cell line HK-2. Stx2-Exo contained pro-inflammatory cytokine mRNAs and proteins and induced more severe inflammation than purified Stx2a accompanied by greater death of target cells such as human renal or retinal pigment epithelial cells. Blockade of exosome biogenesis using the pharmacological inhibitor GW4869 reduced Stx2-Exo-mediated human renal cell death. Stx2-Exo isolated from human primary monocyte-derived macrophages activated caspase 3/7 and resulted in significant cell death in primary human renal cortical epithelial cells. Based on these results, we speculate that Stx-containing exosomes derived from macrophages may exacerbate cytotoxicity and inflammation and trigger cell death in toxin-sensitive cells. Therapeutic interventions targeting Stx-containing exosomes may prevent or ameliorate Stx-mediated acute vascular dysfunction.

Short-chain fatty acid mitigates adenine-induced chronic kidney disease via FFA2 and FFA3 pathways

Short-chain fatty acids (SCFAs), including acetate, butyrate, and propionate, are produced when colonic bacteria in the human gastrointestinal tract ferment undigested fibers. Free fatty acid receptor 2 (FFA2) and FFA3 are G-protein-coupled receptors recently identified as SCFA receptors that may modulate inflammation. We previously showed through in vitro experiments that SCFAs activate FFA2 and FFA3, thereby mitigating inflammation in human renal cortical epithelial cells. This study used a murine model of adenine-induced renal failure to investigate whether or not SCFAs can prevent the progression of renal damage. We also examined whether or not these FFA2 and FFA3 proteins have some roles in this protective mechanism in vivo. Immunohistochemical analyses of mouse kidneys showed that FFA2 and FFA3 proteins were expressed mainly in the distal renal tubules and collecting tubules. First, we observed that the administration of propionate mitigated the renal dysfunction and pathological deterioration caused by adenine. Consistent with this, the expression of inflammatory cytokines and fibrosis-related genes was reduced. Furthermore, the mitigation of adenine-induced renal damage by the administration of propionate was significantly attenuated in FFA2−/− and FFA3−/− mice. Therefore, the administration of propionate significantly protects against adenine-induced renal failure, at least in part, via the FFA2 and FFA3 pathways. Our data suggest that FFA2 and FFA3 are potential new therapeutic targets for preventing or delaying the progression of chronic kidney disease.

Metformin rescues Parkin protein expression and mitophagy in high glucose-challenged human renal epithelial cells by inhibiting NF-κB via PP2A activation

Our preliminary research revealed that metformin, a classic anti-diabetic drug, could rescue Parkin protein expression and mitophagy in high glucose-challenged human renal epithelial cells in vitro, but the molecular mechanism remains to be explored. In the study, Human Renal Cortical Epithelial Cells (HRCEpiC) and Human Renal Proximal Tubular Epithelial Cells (HRPTEpic) were challenged with high glucose with or without metformin pre-treatment to monitor Parkin mRNA and protein expression level change. PRKN gene knockdown was performed by lentiviral-based shRNA delivery. Cell viability, apoptosis and mitophagy were monitored after treatment. Mitochondrial damage was evaluated by analyzing mitochondrial permeability transition pore opening, membrane potential change, mitochondrial superoxide accumulation and cytochrome C release. Protein levels of activating transcription factor 4 (ATF4), p53 phospho-Ser15, IκBα phosphor-Ser32, IKKα phosphor-Ser176/180 in whole cell lysate and nuclear entry of p50/p65 were assessed by western blot. Okadaic acid was used to inhibit protein phosphatase 2A (PP2A). The data suggested high glucose challenge significantly reduced PRKN gene expression, mitophagy, mitochondria integrity and cell viability in vitro, which was rescued by metformin co-treatment. The effects of metformin were crippled by PRKN gene knockdown. Metformin increased PRKN gene transcription while reducednuclear factor kappa B (NF-κB) activation but not that of p53 or ATF4. Inhibiting PP2A weakened NF-κB inhibition and PRKN induction by metformin in high glucose-challenged cells, reducing its mitochondrial protective and cytoprotective effect. So, we concluded thatmetformin protects human renal epithelial cells from high glucose-induced apoptosis by restoring Parkin protein expression and mitophagy via PP2A activation and NF-κB inhibition.

β-Hydroxybutyrate, a ketone body, reduces the cytotoxic effect of cisplatin via activation of HDAC5 in human renal cortical epithelial cells

Aimsβ-Hydroxybutyrate (βOHB) is a metabolic intermediate that constitutes about 70% of ketone bodies produced in liver from oxidation of fatty acids released from adipose tissue. A recent study showed that βOHB inhibits HDAC1, 3 and 4 (classes I and IIa) in human embryonic kidney 293 (HEK293) cells. Therefore, βOHB could regulate epigenetics via modulating HDACs. However, little is known about the protective effect of βOHB on renal cells through epigenetics. The aim of this study is to investigate whether βOHB reduces cisplatin-induced nephrotoxicity in human renal cortical epithelial (HRCE) cells by modulating HDACs. Main methodsIn this study, we used human renal cortical epithelial (HRCE) cells. The anti-apoptotic effect of βOHB was evaluated using flow cytometry analysis. The expression of apoptosis-related proteins and HDACs was evaluated by western immunoblot. Key findingsThe results showed that βOHB significantly reduced cisplatin-induced apoptosis in HRCE cells. Furthermore, βOHB significantly reduced cisplatin-induced cleavage of caspase-3, acetylation of histone H3, and phosphorylation of AMP-activated kinase. This anti-apoptotic effect of βOHB was markedly attenuated by an inhibitor of HDAC4/5, and βOHB-mediated suppression of cleavage of caspase3 was significantly blocked by siRNA-induced gene silencing of HDAC5. SignificanceβOHB attenuates cisplatin-induced apoptosis by activation of HDAC5 in HRCE cells, suggesting that βOHB may be a new therapeutic agent for cisplatin nephropathy.

Correction to: Dual-Purpose Bioreactors to Monitor Noninvasive Physical and Biochemical Markers of Kidney and Liver Scaffold Recellularization, by Uzarski JS, Bijonowski BM, Wang B, Ward HH, Wandinger-Ness A, Miller WM, and Wertheim JA. Tissue Eng Part C Methods 2015;21(10):1032–1043. DOI: 10.1089/ten.tec.2014.0665

[This corrects the article DOI: 10.1089/ten.tec.2014.0665.].

Effects of Blood-brain Barrier and Simulated metabolic system on Apoptosis of SH-SY5Y Induced by Acrylamide in Vitro

Objective: To evaluate the effect of acrylamide on the apoptosis of nerve cells by integral cell modelling in vitro which simulates the barrier effect and metabolic micro-environment. Methods: A non-contact and co-cultured in vitro blood brain barrier (BBB) model was established by using human umbilical vein endothelial cells (HUVEC) and rat glioma cells (C6) . The trans-endotheilal electrical resistance (TEER) and horseradish peroxidase (HRP) tracer effects were measured to verify the tight connectivity and permeability of the established BBB model. An integrate discrete multiple organ cell co-culture (idMOC) model was established by inoculating the human renal cortical proximal tubular epithelial cells (HK-2) , human normal hepatocytes (L-02) and human neuroblastoma cells (SH-SY5Y) into the self-made multi-organ plate for co-culturing. Then the model was verified by observing the growth curve of various tissue cells under co-culturing or culturing individually. SH-SY5Y cells were exposed to different concentrations of acrylamide directly and indirectly (through BBB model and idMOC model) . The changes of cell apoptosis rate were analyzed by flow cytometry to explore the impact of model on Acrylamide (ACR) injury of typical neurotoxic agents. Results: HUVEC cells can form a wide range of close-connected complex and then inhibit the external electric field under the cross-endothelial movement, and the mean was lower than that of endothelial cell culture group at 4, 5 and 6 days (P<0.05) ; After 20 min, the penetration rate of HRP in the co-culture group was less than that in the individual culture group, and the difference was statistically significant (P<0.05) , indicating that the barrier function of the co-culture group was higher than that of the individual culture group. All cells can exchange substances through the exchange hole of the culture plate, the cells grow well and there was no obvious death. The growth curve in individual culture group and co-culture group were basically the same, the difference was not statistically significant (P>0.05) . Under the condition of different concentrations of ACR (140, 270 g/ml) , compared with the direct exposure group, the apoptosis rate of the BBB model and the idMOC model were significantly decreased, and the difference was statistically significant (P<0.05) . Conclusion: Based on HUVEC cells and C6 cells co-culture system, a blood-brain barrier model in vitro was established and based on co-culture of HK-2, L-02 and SH-SY5Y, the idMOC model was established. The toxicity and toxic action characteristics of ACR on SH-SY5Y cells were evaluated by validation tests.

Short-chain fatty acids, GPR41 and GPR43 ligands, inhibit TNF-α-induced MCP-1 expression by modulating p38 and JNK signaling pathways in human renal cortical epithelial cells

Short-chain fatty acids (SCFAs), such as acetate, propionate, and butyrate, are produced predominantly by gut microbiota fermentation of dietary fiber. SCFAs are newly identified as endogenous ligands of two orphan G protein-coupled receptors, GPR41 and GPR43, which have the potential to modulate inflammation. Therefore, GPR41 and GPR43 may mediate the link between the gut microbiome status and various disease conditions including renal inflammation. This study aimed at investigating whether SCFAs activate GPR41 and GPR43, and thereby exert anti-inflammatory effects in human renal cortical epithelial cells (HRCEs) as a main component of kidney tissue.Immunohistochemical analyses of human renal biopsy specimens revealed the expression of GPR41 and GPR43 protein in the distal renal tubules and collecting tubules. TNF-α increased the expression of monocyte chemoattractant protein-1 (MCP-1), a potential fibrotic inducer, at least partly via enhancing phosphorylation of p38 and JNK in HRCEs. SCFAs, especially propionate, attenuated TNF-α- stimulated MCP-1 expression by inhibiting the phosphorylation of p38 and JNK. This inhibitory effect was considerably attenuated by an inactivator of the Gi/o-type G protein and a Gβγ (i/o) blocker, but not by a Gα (i/o) blocker. Furthermore, SCFA-mediated inhibition of MCP-1 expression was significantly blocked by siRNA-induced gene silencing of GPR41 and GPR43.In conclusion, SCFAs lowered TNF-α−induced MCP-1 expression by reducing phosphorylation of p38 and JNK in a GPR41/43-dependent manner in HRCEs, suggesting that SCFA modification may be a new therapeutic tool for preventing progression of renal inflammation and fibrosis.

Osteopontin improves adhesion and migration of human primary renal cortical epithelial cells during wound healing

The aim of the present study was to investigate the effect of osteopontin (OPN) on adhesion and migration in human primary renal cortical epithelial cells during wound healing and Transwell assays. MTT assay was used to examine the cell viability and western blot analysis was used to examine the expression of cytoskeletal proteins and cell adhesion molecules. The results showed that overexpression of OPN had positive effects on the viability, proliferation, adhesion and migration of the human primary renal cortical epithelial cells. In addition, the integrity of the cell membrane and cytoskeleton of the epithelial cells was negatively affected by knockdown of OPN expression. The Transwell migration and a wound healing assays performed using OPN-knockdown cells suggested that OPN had a significant impact on cell migration (P=0.0421) and wound healing (P=0.0333). Therefore, OPN may be a potential target for the therapeutic modulation of skin repair to improve the healing rate and quality of wound healing.

Freezing/Thawing without Cryoprotectant Damages Native but not Decellularized Porcine Renal Tissue

abstractWhole organ decellularization of porcine renal tissue and recellularization with a patient's own cells would potentially overcome immunorejection, which is one of the most significant problems with allogeneic kidney transplantation. However, there are obstacles to achieving this goal, including preservation of the decellularized extracellular matrix (ECM), identifying the proper cell types, and repopulating the ECM before transplantation. Freezing biological tissue is the best option to avoid spoilage; however, it may damage the structure of the tissue or disrupt cellular membranes through ice crystal formation. Cryoprotectants have been used to repress ice formation during freezing, although cell toxicity can still occur. The effect of freezing/thawing on native (n = 10) and decellularized (n = 10) whole porcine kidneys was studied without using cryoprotectants. Results showed that the elastic modulus of native kidneys was reduced by a factor of 22 (P < 0.0001) by freezing/thawing or decellularization, while the elastic modulus for decellularized ECM was essentially unchanged by the freezing/thawing process (p = 0.0636). Arterial pressure, representative of structural integrity, was also reduced by a factor of 52 (P < 0.0001) after freezing/thawing for native kidneys, compared to a factor of 43 (P < 0.0001) for decellularization and a factor of 4 (P < 0.0001) for freezing/thawing decellularized structures. Both freezing/thawing and decellularization reduced stiffness, but the reductions were not additive. Investigation of the microstructure of frozen/thawed native and decellularized renal tissues showed increased porosity due to cell removal and ice crystal formation. Orcein and Sirius staining showed partial damage to elastic and collagen fibers after freezing/thawing. It was concluded that cellular damage and removal was more responsible for reducing stiffness than fibril destruction. Cell viability and growth were demonstrated on decellularized frozen/thawed and non-frozen samples using human renal cortical tubular epithelial (RCTE) cells over 12 d. No adverse effect on the ability to recellularize after freezing/thawing was observed. It is recommended that porcine kidneys be frozen prior to decellularization to prevent contamination, and after decellularization to prevent protein denaturation. Cryoprotectants may still be necessary, however, during storage and transportation after recellularization.

Biocompatibility, uptake and endocytosis pathways of polystyrene nanoparticles in primary human renal epithelial cells

Recent years have witnessed an unprecedented growth in the number of applications – such as drug delivery, nutraceuticals and production of improved biocompatible materials – in the areas of nanoscience and nanotechnology. Engineered nanoparticles (NPs) are an important tool for the development of quite a few of these applications. Despite intense research activity, mechanisms regulating the uptake of NPs into cells are not completely defined, being the phenomenon dramatically influenced by physico-chemical properties of NPs and cell-specific differences. Since the cellular uptake of NPs is a prerequisite for their use in nanomedicine, the definition of their internalization pathway is crucial. For this reason, we used 44nm polystyrene NPs as a model to analyze the uptake and endocytosis pathways in primary human renal cortical epithelial (HRCE) cells, which play a key role in the clearance of drugs. NPs were found not to affect the viability and cell cycle progression of HRCE cells. Distinct internalization pathways were analyzed by the use of drugs known to inhibit specific endocytosis routes. Analyses, performed by confocal microscopy in combination with quantitative spectrofluorimetric assays, indicated that NPs enter HRCE cells through multiple mechanisms, either energy-dependent (endocytosis) or energy-independent.

Bioengineered 3D Human Kidney Tissue, a Platform for the Determination of Nephrotoxicity

The staggering cost of bringing a drug to market coupled with the extremely high failure rate of prospective compounds in early phase clinical trials due to unexpected human toxicity makes it imperative that more relevant human models be developed to better predict drug toxicity. Drug–induced nephrotoxicity remains especially difficult to predict in both pre-clinical and clinical settings and is often undetected until patient hospitalization. Current pre-clinical methods of determining renal toxicity include 2D cell cultures and animal models, both of which are incapable of fully recapitulating the in vivo human response to drugs, contributing to the high failure rate upon clinical trials. We have bioengineered a 3D kidney tissue model using immortalized human renal cortical epithelial cells with kidney functions similar to that found in vivo. These 3D tissues were compared to 2D cells in terms of both acute (3 days) and chronic (2 weeks) toxicity induced by Cisplatin, Gentamicin, and Doxorubicin using both traditional LDH secretion and the pre-clinical biomarkers Kim-1 and NGAL as assessments of toxicity. The 3D tissues were more sensitive to drug-induced toxicity and, unlike the 2D cells, were capable of being used to monitor chronic toxicity due to repeat dosing. The inclusion of this tissue model in drug testing prior to the initiation of phase I clinical trials would allow for better prediction of the nephrotoxic effects of new drugs.

Activities of Different Classes of Acyclic Nucleoside Phosphonates against BK Virus in Primary Human Renal Cells

BK virus (BKV), a virus belonging to the polyomavirus family, is a circular double-stranded DNA virus that causes nephropathies in immunocompromised patients after kidney or bone marrow transplantation. The occurrence of polyomavirus-associated nephropathy in kidney transplant patients may trigger graft loss, and guidelines for the management of BKV infection have not yet been clearly established. Treatment of BKV nephropathy with cidofovir (CDV) {(S)-1-[3-hydroxy-2-(phosphonomethoxy)propyl]cytosine (HPMPC)}, an acyclic phosphonate analogue of dCMP with a broad antiviral activity against DNA virus infections, has been proposed. The benefit of this small-molecule-based treatment has been evaluated only with a limited number of cases. In this study, we report the evaluation of three different classes of acyclic nucleoside phosphonates for their activities against BKV replication in two different primary renal cells: renal proximal tubular epithelial cells (RPTECs) and human renal cortical epithelial (HRCE) cells. The data indicate that besides HPMPC and its cyclic form, (S)-1-[3-hydroxy-2-(phosphonomethoxy)propyl]-5-azacytosine (HPMP-5-azaC), cyclic HPMP (cHPMP)-5-azaC, hexadecyloxyethyl (HDE)-cHPMP-5-azaC, and 9-[2-(phosphonomethoxy)ethyl]guanine (PMEG) are the most selective inhibitors of BKV replication. On the contrary, leflunomide, which has also been proposed for the management of BKV-associated diseases, is not able to inhibit BKV replication at nontoxic concentrations.

Chronic renal allograft dysfunction: the role of T cell-mediated tubular epithelial to mesenchymal cell transition.

Chronic graft dysfunction is now the leading clinical problem after renal transplantation. The principal histopathologic lesion seen in this disease is tubular loss with concurrent interstitial fibrosis. Although the severity of acute rejection often correlates with that of subsequent chronic dysfunction, a direct link between these processes has remained elusive. This study was designed to test the hypothesis that intraepithelial T cells recruited to the renal tubules during acute rejection can directly induce fibrosis by causing tubular epithelial cells to undergo transformation to produce a motile population of activated fibroblasts. A study of renal allograft tissue sections showed the presence of the S100A4 marker of epithelial to mesenchymal transition in some tubular epithelial cells; the expression of this antigen was heterogeneous both within and between individual tubular cross-sections. Significantly, S100A4-expressing epithelial cells were frequently associated with infiltrating CD8+ T cells, and many coexpressed the Ki67 marker of proliferation. A parallel study of human renal cortical epithelial cells in primary culture demonstrated that S100A4 was induced by stimulation for 72 h with TGF-beta(1) and by direct contact with membrane-associated TGF-beta on MOLT-16 cells, a model intraepithelial T-cell line. Further experiments demonstrated that induction of transition coincided with a significantly increased potential for human renal epithelial cells to invade the tubular basement membrane. These data are consistent with a model in which intratubular T cells can present TGF-beta and directly induce adjacent tubular epithelial cells to transform to proliferating fibroblasts that migrate across the tubular basement membrane, producing fibrotic lesions within the renal interstitium.

Inhibition of shiga toxin cytotoxicity in human renal cortical epithelial cells by nitrobenzylthioinosine.

Nitrobenzylthioinosine (NBTI), a nucleoside-transport inhibitor, has been found to possess the ability to prevent the cytotoxic action of Shiga toxin (Stx) 1 in human renal cortical epithelial cells (HRCECs), thereby protecting HRCECs from cell death. Further examination revealed that NBTI does not affect either the binding or the endocytosis of Stx1 but alters the intracellular transport of Stx1. Generally, endocytosed Stx1 is thought to be transported from endosomes to the endoplasmic reticulum. In NBTI-treated cells, however, the endocytosed Stx1 is delivered to an early endosome, but no further transportation occurs. Moreover, Stx1 is rapidly excreted from NBTI-treated HRCECs, preventing the accumulation of Stx1. Investigation of the NBTI-mediated protection mechanism against Stx cytotoxicity may provide insights into the analysis of Stx-mediated cell damage and lead to improvements in therapeutic approaches for diseases caused by Stx.

Induction of apoptosis in normal human renal tubular epithelial cells by Escherichia coli Shiga toxins 1 and 2.

The cytotoxicity of Shiga toxin (Stx) 1 and Stx2 produced by Escherichia coli to human renal cortical epithelial cells (HRCEC) in primary culture was investigated. HRCEC express CD24, the marker of renal distal tubules, as well as globotriaosyl ceramide/CD77, the receptor for Stxs. Binding of Stxs to HRCEC was confirmed by positive staining with specific antibodies to Stxs. Treatment of HRCEC with Stxs induced rapid cell death, which was reversed in the presence of neutralizing antibody specific for Stx. DNA fragmentation was found to be accompanied by Stx-mediated cell death in HRCEC, indicating that apoptosis was part of the process. These data and previous reports indicate that a variety of renal cell types, including tubular epithelial cells as well as glomerular capillary endothelial cells, may be targets for Stx-mediated apoptosis, which could contribute to the pathogenesis of hemolytic-uremic syndrome caused by Stx-producing E. coli infection.

Endothelial cell associated platelet-activating factor (PAF), a costimulatory intermediate in TNF-alpha-induced H2O2 release by adherent neutrophil leukocytes.

TNF is a strong secretagogue for surface-contacting neutrophils. During inflammation, endothelium offers the first substrate for neutrophil adherence and for modulation of the toxic response of neutrophils to soluble agonists such as TNF. In this in vitro study, evidence is presented that endothelium participates actively in TNF-induced neutrophil respiratory burst activity by expressing platelet-activating factor (PAF) in response to initial neutrophil H2O2 release. Three findings are shown that favor such a mechanism. First, PAF receptor antagonists reduced H2O2 release by TNF-activated neutrophils placed on endothelium approximately by 50%, whereas H2O2 responses by neutrophils placed on serum-coated polystyrene remained intact. Second, preincubation of HUVEC with known PAF-inducing agents PMA, H2O2, and thrombin, followed by fixation, enhanced neutrophil H2O2 release in response to TNF. H2O2 release by these neutrophils was sensitive to the presence of PAF receptor antagonists, whereas H2O2-release from neutrophils placed on fixed nonactivated endothelial cells was not. Finally, replacing endothelium by monolayers of human renal cortical epithelial cells and human fibroblasts, cells that are known to produce less PAF than endothelial cells, reduced the effect of PAF receptor antagonists. P-selectin expression and IL-8 release, two other ways by which endothelial cells might influence H2O2-release by TNF preincubated neutrophils, were examined in parallel, and were found not to influence TNF-induced neutrophil H2O2-release. We conclude that during neutrophil-endothelial interaction in inflammation, endothelium modulates the toxic response of neutrophils to TNF. Endothelial cell-associated PAF, but not endothelial cell IL-8 release and P-selectin expression, is likely to participate in TNF-induced neutrophil respiratory burst activity.

Epithelial-derived neutrophil-activating factor-78 production in human renal tubule epithelial cells and in renal allograft rejection.

Chemotactic cytokines, or chemokines, are likely mediators of inflammatory cell recruitment in renal allograft rejection. A recent addition to the C-X-C super gene family branch of chemokines is epithelial-derived neutrophil-activating factor-78 (ENA-78). ENA-78 is a 78-amino acid peptide with neutrophil-activating and chemotactic properties. This chemokine is unique in that it was originally isolated and cloned from an IL-1-stimulated human pulmonary epithelial cell line, A549. In this article, we investigated whether ENA-78 could be produced by human renal epithelial cells. We found that primary cultures of human renal cortical epithelial cells with tubular cell attributes could express significantly increased steady state levels of ENA-78 mRNA when stimulated with IL-1 beta (2.0 ng/ml). In addition, these cells also secreted significantly increased ENA-78 antigen compared with controls when stimulated with IL-1 beta (2.0 ng/ml). Other proinflammatory agonists, including TNF alpha, IFN gamma, and LPS failed to stimulate ENA-78 steady state mRNA or antigenic peptide production by renal cortical epithelial cells. In addition, biopsy tissue from acutely rejecting human renal allografts had higher copy number of ENA-78 mRNA compared with nonrejecting renal allograft controls using a quantitative reverse transcriptase polymerase chain reaction method with a mutant ENA-78 transcript. In the proinflammatory milieu of the rejecting renal allograft, IL-1 beta produced by host and donor mononuclear cells may drive ENA-78 production by allograft tubule cells, thus effecting leukocyte recruitment into the tubulointerstitial compartment.